The insertion of the weft thread into the loom shed requires an accurate precise operation of the weft thread insertion device. U.S. Pat. No. 4,878,392 (Jaeger et al.), published on Nov. 7, 1989 discloses a gear drive for shuttleless looms of the types here involved. Such gear drives comprise components which convert the rotational continuous movement of the main loom drive shaft into a back and forth movement of the weft thread inserting device. These components produce two rotational movements that are alternatingly directed in opposite directions and these opposite rotational movements are in turn converted into the linear back and forth movement of the weft thread insertion devices.
The above mentioned gripper heads that are either carried by gripper rods or flexible tapes are so arranged that one gripper head carries the weft thread half way into the loom shed and the other gripper head carries the weft thread all the way out of the loom shed. The rods or tapes with the gripper heads enter and exit the loom shed from the opposite sides to carry the weft thread completely through the loom shed. Different conventional devices for the just described weft thread insertion are known in the art. Only the drives for these insertion devices are of interest to the present invention.
Flexible tapes are, for example, wound up on disks that are driven in one direction or in the opposite direction. Similarly, gear wheels may engage a toothed rack that forms the gripper head carrying rod. Gear wheels engaging perforations in the flexible tapes carrying the gripper heads are also known. The gear drives used for the just described purpose comprise conventionally a first gear section for converting the continuous unidirectional rotation of the main loom drive shaft into oppositely directed rotations, and a second gear section for transmitting the oppositely directed rotational movements to the respective weft thread insertion device. The first gear section comprises continuously rotating cams cooperating with cam followers which in turn drive a piston rod type connecting rod which drives a gear sector, whereby the gear sector performs an oscillating back and forth motion. The second gear section in turn transmits the back and forth motion of the gear sector through gear components to the weft thread insertion devices, whereby any required r.p.m. translation will be performed. For example, the second gear section includes a drive wheel that meshes with a gear or rack section of a gripper rod or that meshes with perforations in a flexible tape carrying a gripper head. If required, angular gears are used to change the direction of power transmission. Thus, the oscillating motion of the gear sector is transformed into an alternating rotational movement of the gear wheel driving the insertion device. The stroke of the back and forth movement can normally be adjusted by adjusting the connection of the connecting rod to the gear sector. These adjustments make it possible to precisely determine the extent to which the gripper heads move into and out of the loom shed. These adjustments thus make it possible to vary the motion of the gripper heads in accordance with the required weaving width.
Conventionally, a single output drive shaft, and thus a single output drive wheel, transmits the alternating back and forth motion to the gripper rod or tape. Due to the continuous direction reversal the components involved in the direction reversal and drive are subject to substantial wear and tear. Such a single wheel drive also exposes the gripper rod or gripper tape to excessive wear and tear. Thus, there is room for improvement in the just described conventional drives.